For power semiconductor devices (e.g., BJT, MOSFET, thyristor, IGBT, etc), the safe operating area (SOA) is defined as the voltage and current conditions over which the device can be expected to operate without self-damage. By way of example, the damage to the device can occur if VD exceeds the SOA boundary. By way of a more specific example, operating outside of the SOA boundary can be caused by large varying current components, which result in electromagnetic interactions causing damage to the device. Many factors can cause the device to operate outside of the safe operating area (SOA) boundary including, e.g., device dimensions, current, location of metal lines, etc. Moreover, abnormal SOA/resistor-like behavior can occur at a high VGin for both RF and power transistors.
The skin effect and proximity effect are also known to effect device performance, e.g., for a device to perform outside of the SOA boundary. For example, skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor, and decreases with greater depths in the conductor. The skin effect causes the effective resistance of the conductor to increase at higher frequencies where the skin depth is smaller, thus reducing the effective cross-section of the conductor. For current flowing in the same direction, the currents will crowd at the two edges; whereas, for current flowing in different directions, the currents will crowd at the regions facing each other.
On the other hand, the proximity effect in a conductor carrying alternating current results from currents flowing through one or more other nearby conductors. In the proximity effect, distribution of current within the first conductor will be constrained to smaller regions, resulting in current crowding. This crowding gives an increase in the effective resistance of the circuit, which increases with frequency.